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Why is there such a low level of automation in the aerospace industry (compared to other industries such as automobile)?
I have been watching some episodes of the documentaries made by National Geographic lately and I have noticed something that I can't find an explanation for.
In this episode of Megafactories - Eurofighter Typhoon, starting at 17:21, the amount of automation in the factory is apparently very low and the workers seem to be doing everything with their hands.
On the contrary, in this episode about the Volkswagen factory in Wolfsburg, starting at 24:05, the process is much much more automated and there is almost no one around doing anything by hand.
I have always thought that the aerospace industry is one of the most sensitive industries and the highest levels of accuracy, precision and consistency are required. But those documentaries show the opposite to this.
So is there a reason as to why this Eurofighter Typhoon factory is so much less automated than this Volkswagen one? Is there something I might be missing that would make a less automated factory a better choice for the aerospace industry?

Automation doesn't imply accuracy or consistency. For accuracy and consistency you need quality control. But automation does requirement huge upfront investment which can only be recovered by a large throughput, which Typhoon, with a grand total of 565 units built, obviously doesn't have.

A Rolls-Royce is typically mostly hand-built. Would you consider that lower quality compared to a VW? I bet the Rolls-Royce has higher "levels of accuracy, precision and consistency" in their products, but automation just isn't worth it with so few being produced.

@Bianfable, a comparison of Rolls-Royce and VW is a bit confusing for a couple of reasons. See, Rolls-Royce, in context of this site, usually means the direct descendant of the original company that now makes exclusively turbine engines (including third of those that go in Typhoons). The car division got split out a long ago, and was bought by none else than VW. It only makes cars under the brand Bentley though, because the trademark for cars was bought by BMW, which now has a new subsidiary that also has Rolls-Royce in its name, but no relation to the original comany.

@JanHudec I am fully aware of that, but I don't think anyone would confuse what I meant. Comparing a Rolls-Royce with a VW is clearly about cars, not engines.

There are two big factors at play here: scale and throughput.
First, automation is very good at repetitive tasks. The Wolfsburg plant produces over 800,000 cars per year. It's taken 25 years to make almost 600 Typhoons. That means yearly production is different by four orders of magnitude. It's a lot easier to justify the cost of buying, installing, and programming a robot to save a human from doing the task 800,000 times in a year than just 25 times. This also means that a robot can completely replace a person with a job at one place on the assembly line doing only a few tasks over and over. On the Typhoon line, even if a person only works one line position, they may have many more tasks all over the airplane.
The scale of the Typhoon is also different. It's easy for a few standard industrial robots to access an entire car chassis. It's much harder to access everything on a fighter jet. Larger robots will be even more expensive. Mobile robots are much harder to use with high accuracy. And where you might be able to have multiple humans doing various tasks in the same area, the whole area would have to be blocked off for safety to allow maybe a couple robots to work there.
There is also the factor of processes. A lot of the assembly work on cars is done with welding, which is fairly simple for a robot to do. The Typhoon is mostly assembled with nuts and bolts, which is a much more complex process for a robot to accomplish.
If you break things down to the component level, the balance changes. Drilling thousands of holes in the various components is often done with robotics and some smaller assembly work can be done as well. It's where all of that is assembled into a large structure that humans become the cheaper option.
This also feeds back into the design process. Cars are designed from the start to be easily assembled robotically, because it's much cheaper that way. Not having to design all assembly processes around robot access allows aircraft designers to make things smaller and lighter, a much larger factor for airplanes than cars.

The difference is that airplane construction is a bit closer to house construction x100 than making cars.
Cars: Small objects made of a relatively small number of largely preformed parts bolted together.  Many operations can be performed by a stationary robot doing the same repetitive things that an assembly line worker did.  Easy and cheap to automate as industrial robots were developed.
Airplanes:  Large objects made from vast numbers of pieces, with even vaster number of fasteners and components.  The people doing the assembly have to be very mobile and flexible in their activities.   This is very hard to automate compared to creating a machine that can sit in one spot and perform a job previously doable by a low IQ human.  Just the riveting process requires 2 people to perform (except for small assemblies where a worker can reach both sides), requiring a certain amount of skill and abstract thinking and judgement, and who need to have a fair amount of freedom of action.  Requires a far higher level of robotic sophistication compared to cars.
That being said, the latest aircraft production lines are become a lot more automated, relatively speaking, with things like integrated whole-fuselage robotic riveting machines, sub-assembly riveting robots, automated component movers.  The production line for the A-220/C-Series has quite a bit fewer people around it than the traditional one, although it's still an ant farm compared to an automotive line.


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What are the equation linking static air temperature with true airspeed & altitude?
If I want to calculate static air temperature (OAT), but I'm only given an altitude and a true airspeed. Is there such an equation that relates these principles together. I've had a look at wikipedia and to calculate OAT, the total air temperature is required. Problem is, I don't have a Mach number to solve the equation. Is there another way to solve this problem

And to know the Mach # you need the static air temperature... a circle of doom question I'd say...

You don't have calibrated airspeed? How do you get true airspeed without the calibrated airspeed?

OAT and pressure altitude (PA) lets you compute density, from which you can relate calibrated airspeed (CAS) and true airspeed (TAS). So if you know any three of OAT, PA, CAS, and TAS, you can get the forth. Right now you are short a piece of information in order to "close the loop" and get OAT. Note: I am assuming you are at a slow speed and can ignore Mach number.

Provided that your calculations take place for a standard day, below 11 km altitude the Outside Air Temperature is simply a linear function of altitude. From the wikipedia article for Standard Atmosphere:

So OAT = 15 - 1.98 * Altitude, with OAT in °C and Altitude in 1,000 ft. Airspeed data is superfluous.

With a big emphasis on standard (average) day, with delta ISA being zero.

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Can a CFM56-3C engine be converted into a CFM56-3B1?
Is it possible to take a CFM56-3C engine and modify it to a CFM56-3B1 engine? I own a CFM56-3C engine but my customer would like to install a CFM56-3B1 engine on his plane. Can this be done?

A good subquestion would be : how common are those engines? If there are too many parts that differ, it may be hard (technically and legally) to convert one into the other.

This question raises so many other questions...

In theory, I think that should be possible, as the -3B is a lower thrust rating than the -3C (going to higher thrust rating would be harder).  However, you would have to ask CFM.  I think they are the only ones that could answer.

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How to compute drag coefficient for falling book?
The book measures 20 x 20.3 x 1.4cm and I'm assuming it's sealed shut so the pages don't flap open. Mass is 450g.
I want to understand how quickly it would fall if dropped straight down from 10km altitude. I've used a value for drag coefficient for a flat plate perpendicular to the air flow that I got from NASA (1.28) but I'm guessing that a falling book would spin round, slowing its fall, so this value is probably not right - is this likely?
So I'm wondering if it's possible to estimate the drag coefficient to any degree of accuracy. I don't have access to a wind tunnel and I'd rather not drop it off a tower as an experiment. :)

Umm.. if the book tumbles and spends part of its time falling with say the spine pointing straight down, won't the average speed be much faster than suggested by your description?

I don't get the downvotes, this is less ridiculous than other questions on the site, and makes for an ok though experiment.

Brings to mind a new possible question :"what is the purpose of a book"-- similar to "what is the purpose of a propeller"

Try physics.se for relevant answer as well.

@AEheresupportsMonica and others: this question is being discussed here: https://aviation.meta.stackexchange.com/q/3978/1467

Sorry but non-aviation aerodynamic questions are off topic here, see the [help] and linked meta post for more info.

You have a very thin book. The answer depends on how you initially drop the book.
1. If you drop it flat about its front
It will very closely approximate a flat plate; in this case, the pressure drag will overwhelm the skin friction drag. Hoerner, Fluid Dynamic Drag has some empirical data on the drag coefficient of a bluff body (near 2.0):

To retrieve the 3D coefficient, dimensionalize it with the frontal area.
2. If you drop it broadside
The skin friction drag would dominate. You can approximate it via the flat plate friction drag. For a single side, the drag coefficient looks like (from Anderson, Fundamentals of Aerodynamics):

3. If it tumbles
Your book may also tumble at some point due to random perturbation about its major principal axis. This changes the drag even further; but once again, Horner has some empirical correction formula.

The book's pages won't flap open, but it will bend unpredictably, because its density is so close to that of paper (vs. hardboard) that it must be a paperback.  So you can't assume that it's a flat plate. Even if you fling it like a frisbee so centrifugal force holds it flat like LightSail 2, during a 10 km drop, air friction will overcome that and let it tumble chaotically.
I know of no drag measurements for variously curved thin plates at arbitrary angles of attack.  You might need to drop half-ounce paperbacks late at night in a tall building lobby to estimate lower and upper bounds for CD.

Thanks - it is in fact a hardback with 2mm board.

Huh.  Densities for hardboard that I found were a good deal less than for paper, but if these numbers come from your actual measurements, then you'd know!


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Does the flap settings for the best lift/drag ratio change with speed on the Diamond DA20-A?
As I've recently started time building in DA20, I've noticed the AFM suggests flaps at T/O for a glide. Being very intrigued by this I run across this post. Although I appreciate Peter's reply that does throw some light I'm not quite clear with it and I'd like to elaborate on it further. As the topic is closed, and the forum advises against asking for more clarification, I open a new topic here.
Diamond DA20-A1 FM says:
Climb

Wing Flaps: T/O or UP
Airspeed:   65 kts

further elaborating with a table:

altitude:      0-4000 ft, flaps T/O:  65 kts, flaps UP:  69 kts
altitude:   4000-7000 ft, flaps T/O:  63 kts, flaps UP:  65 kts
altitude:  7000-10000 ft, flaps T/O:  62 kts, flaps UP:  -- kts
altitude: above 10000 ft, flaps T/O:  59 kts, flaps UP:  -- kts

Cruise

Throttle:  as required
Prop. Speed Lever:  1900 - 2400 RPM
Wing Flaps: UP

Gliding

Wing Flaps:  T/O
Airspeed at 1609 lbs (730 kg) (vIAS): 72 kts

I deduce there is a speed below which flaps at T/O create more lift than drag and it is therefore beneficial to have them down, however in the whole ATPL syllabus  I've never run across such a thing - a specific speed at which lift/drag ratio for flaps down changes.
I can understand it's either up or down for the best L/D ratio but I don't get why does it change at a specific speed? Unless the reason is the limitation by Vfe (81 kts) when pilot eventually must retract the flaps even at the cost of lower L/D ratio. If that is the reason, then I don't understand why would someone design a wing that's less efficient to fly in Cruise then in Climb?
So, my final question: does the flap settings for the best lift/drag ratio change with speed, or the wing is not flying at its best efficiency in cruise?
Besides, if we compare climb with gliding speed, we can see that in a climb flaps are to be retracted at 69kts (and even lover as altitude increases), while in glide they are to be at T/O position at 72kts. Where does this difference come from?

Ok, whole two hours, no answers and there's a question regarding the whereabouts of ppl. It's weekend dude, I hope folks are outside having fun  But seriously, a good question (the one about flaps that is), I was stupid enough not to wonder this myself some years ago. I do not have a definitive answer, but my intuition is that it has to do with the DA's being very slippery planes. They just love to fly, where some other planes I'm familiar with tend towards the gnd when not powered... I thinks @Addullah might be onto smthng in his answer.

The linked question definitely isn't closed, and asking Peter to elaborate further in a comment on his answer is probably most likely to get you the clarification you want.

@JanHudec You're right, the post is still open. Initially I tried to comment on Peter's answer however I was unable to as I need at least 50 reputation. Then I tried to give an answer however the pop up message advised against answers which actually ask for clarification, instead of giving an answer.

You did the right thing when asking a new question. Comments are poorly suited for the explanation of non-trivial issues.
Now follow several links to older answers. They should help to explain a couple of things, such as:

what flaps do to L/D.
how thrust changes over speed for propeller aircraft.
and how efficient propeller airplanes are in cruise.

does the flap settings for the best lift/drag ratio change with speed?

Below you see the polar plot from the first linked answer. It shows the airfoil drag in 2D flow. Clearly, the best L/D is achieved with the +10° flap setting, but at this setting the airfoil becomes rather poor below a lift coefficient of 0.3. In order to reduce drag, the flap should be raised when flying fast enough so that the lift coefficient drops below that value.

So the answer is yes, the optimum flap setting does change with speed. Only the flap setting for the overall best L/D will be found at the same flap setting, but then this best L/D can only be reached at one specific lift coefficient (which is equivalent with one specific speed if mass does not change).

I can understand it's either up or down for the best L/D ratio but I don't get why does it change at a specific speed?

It does not change at a specific speed. It changes continuously with lift coefficient (and, implicitly, speed). If you compare specific flap angles, you will find crossover points when the L/D of one flap setting drops below that of another flap setting as the lift coefficient changes. Normally, airplanes only allow a few specified flap angles, so it might seem that L/D changes abruptly when changing flap angles. However, flaps could also move continuously, adapting the wing to its optimal setting for each operating point.

why would someone design a wing that's less efficient to fly in Cruise then in Climb?

Cost. GA aircraft don't have the complex flap systems of airliners and, consequently, have a much larger wing than what is required for cruise. Wing area is sized for the mandated minimum airspeed of 61 kts or less and installed power means that the airplane at low level cruises at a speed where friction drag dominates and induced drag is almost negligible. While technically possible, the complex high-lift systems of airliner wings would make any GA airplane a lot more expensive, a death trap for untrained pilots and a maintenance nightmare.

@Flion The syllabus is right: The best L/D is indeed achieved with the clean configuration. Vary speed and you will vary L/D, and now there might be some flap setting where L/D at that speed is better with flaps than in the clean configuration. This is possible at very low speed when the clean configuration almost stalls.

Thanks Peter. This was very informative and quite strange that in the whole ATPL syllabus there's not even a slight hint that the best L/D flap setting changes with speed. It always teaches that the best LD ratio for the aircraft is always in clean configuration.
Interesting to see the polar diagram with a double change in CL (0.4 to 0.9 for flaps +10) for no change Cd. I've always observed it as a curved line with interdependence of coefficients. I wonder now how the polar diagrams for DA-20 and C-172 compare, as the latter glides with flaps up. Any source for these?

@Flion: The polar here is for the airfoil only. A full airplane polar is dominated by induced drag which has that curved line as drag increases with the square of lift. This induced drag is missing here to make more obvious what flap settings do.

@Flion: The difference between C-172 and DA-20 is how zero flaps are defined. In the C-172, zero is when the flap is in line with the rest of the wing. In the DA-20 zero is actually a negative setting and the equivalent to the C-172's zero is a positive deflection. The original DA-20 airfoil was designed for high lift and is unsuitable for fast flight. HOAC added a 20% flap to widen its useable lift coefficient range. It needs that negative deflection to improve drag in cruise and in order to not confuse pilots, the zero point was shifted to that position.

Thanks a million Peter. I'm curios, why would a full airplane polar add more induced drag? Shouldn't a fuselage add more parasitic drag? I think of induced drag as something that comes as an adverse effect of lift, which is what wings create (although a fuselage can create some lift as well).

Peter thanks a million for your informative answers however I'm still having difficulties grasping this fully. Looking at this polar, I'd deduce that this is not isolated case for DA-20 only. I'd say that for every wing and therefore every airplane, the best L/D ratio changes with speed and there would be a speed for which eventually best L/D is with flaps down - which is not the case. Why is this airfoil special in a way that drag does not increase with flaps (not talking about L/D ratio, just drag)?

For example, looking at the Airbus A320 drag polar, it is clear that drag changes with any change of flaps setting. In your example, the drag remains (relatively) constant with only lift changing.
https://www.researchgate.net/profile/Tomas_Melin/publication/260198739/figure/fig17/AS:558387171688448@1510141284769/Drag-polar-of-an-Airbus-A320-in-three-different-flap-settings.png


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What should be done in case of the avionics failure?
Yesterday I was flying in my simulator with the Cessna 172 when I thought about simulating a fault in the plane's electrical system (alternator and master). But then I was in doubt, if I can't contact the tower or enter a code on the transponder, how can I inform that I need to land on a runway?

Sim flying aside. If you are flying in real life, a backup handheld NavCom radio is a good investment. Like insurance, it’s not worth the cost until you need it. Make sure you get the headset adapters.

The 172 includes a battery that will suffice for a radio transmission. The radio system is on the essential bus, meaning it will function even when most of the systems are cut off. It's 15-30 minutes of power, which is still enough to signal an emergency.

@ZOMVID-20 - Very true. Sometimes even longer if you do not have a huge electrical load. I’ve made it all the way back to my home airport at night in a 172M after losing an alternator by turning off everything but my position lights, anti-collision lights, beacon and Com2. I chose there instead of a much closer unattended airfield with power lines at the end of the runway because I knew our airfield had 24 hour security with airband and police band radios in their cruiser.  Check this out from AOPA’s Air Safety Institute Called Powerless Over Paris.   https://youtu.be/UQtvi1ijPQ4

P.S. The generally accepted power reserve for a GA 6-pack battery is 30 minutes. A G1000 standby battery’s is one hour. Don’t count on even a minute of reserve power. Anything over a minute is gravy. You don’t know the true health of that battery. Nor, do you know the actual time a low voltage condition existed. Make your radio calls, reduce electrical load, and land ASAP.

In the U.S. (other jurisdictions may be similar)...
Avionics are a convenience in VFR day flight. You should be able to fly your airplane by sight picture alone. There are aircraft flying today without any electrical system at all. In a fixed-gear aircraft, none of the equipment required by Part 91.205(b) require electric power. There are standard protocols in place if you have to fly to a destination without electric power.
If you are not on a flight plan or flight following when you lose electric power, stay clear of Classes A, B, and C airspace as well as the 30 nautical mile mode C veil around Class B airports, and the airspace above Class A, B, and C. Stay or descend below 10,000 feet MSL if possible or 2500 feet AGL when not possible to descend below 10,000 feet MSL.
If you lost all electric power before communicating your situation and intentions to ATC, you can assume that squawking 7600 on your electric transponder will do no good, either. Find a VFR Class D, E, or G airfield where you can land. Land as soon as practicable. Remember, you can not enter Class D airspace (normally a 4 mile radius from the field) until you have established two-way communications with them. You can, however, circle above the traffic pattern or tower at an altitude outside of the usually 2500 foot AGL ceiling of Class D until you get light gun signals from the tower. Wagging your wings or following their instructions will be your acknowledgement of light gun signals. Two-way communication will then be established.
Remember, an active IFR plan will give you clearance to your declared destination or declared alternate(s) at your ETA. Neither a VFR flight plan nor flight following prior to an expressed clearance will give you clearance into A, B, C or D airspace.
You should follow this plan of action at any Class D, E, or G airport with an operating control tower. Typically (but not always), a Class E or G airfield will not have an operating control tower. At those airfields, follow the AIM recommendations for entering the traffic pattern for a landing. An overhead flyover well above traffic pattern altitude would be advisable beforehand. Be very cautious of existing traffic. And, make your flight path as predictable to other pilots as possible. Although communication is strongly recommended, it is not required.
If you are flying on an IFR flight plan in IMC, follow the directions of Part 91.185.
If you are flying VFR at night, make it a habit to have the phone numbers of nearby towers, TRACON, and ARTCC in your cell phone. Call them to tell them of your predicament. Declare an emergency via cell phone. Then, use your Part 91.3 PIC authority to request clearance to land at any airport where the runway lights will be lit regardless of airspace or class. ATC can coordinate your clearances, then call an airport official or radio a passing airborne aircraft to turn the light on for you. You won’t be able to do it yourself without an operating radio. And, landing at a dark airport without a landing light will be challenging at best.

Also there is no reason the mobile phone wouldn't work by day if it will by night (and light GA aircraft are slow enough and fly low enough that it should work fine). Any mean of communicating with the ATC counts.

@JanHudec - Good point. Although, even below 5000 feet AGL, reception can be spotty. One consideration that I would make would be to only call Class D airports in a non-emergency. Day VFR Nordo to me is not an emergency. Night VFR or any type of IMC without a backup handheld NavCom, and without electricity, would be an emergency. I suppose if you are already inside A, B or C airspace, or in a VFR corridor, it would be a judgement call on whether to try the phone or seek Class E or G airspace.

If you have a total electrical failure, then you should try to find a suitable non-towered field to land at. In a C172, you have about 15,000 choices in the US, and unless you're in the mountains, probably only a few minutes away from a decent one. The number of choices goes down as aircraft size goes up, but there shouldn't be any trouble finding one as long as your engine is still running. Since a radio isn't required at non-towered airports anyway, just enter the pattern and land as usual.
If the only suitable airport is a towered one, then head directly there well above pattern altitude, circle the field, watch for light gun signals from the tower, and then land when they tell you it's safe.
Next time you're at a (real) towered airport on a slow day, ask them to demonstrate the light gun so you know what it looks like. I don't know if sims have that feature, though.

You might insert a "try frantically to remember those light-gun signals that you learned several decades ago to pass you written, but haven't thought about since".

@jamesqf - That’s what kneeboarding are made for .

@jamesqf By the time you're low enough to see the light gun, you should have cellular reception and be able to Google what it means. Or better yet, look up the tower's phone number!

I meant kneeboards...

@StephenS: Assuming of course that you have a cell phone with you.

I was wondering, @DeanF. if "kneeboarding" was like "waterboarding", but inflicted on the legs... ;)


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Does the jet blast from a large aircraft pose any risk for other aircraft nearby?
We know that the jet blast of jetliners - A320, B737 and bigger - are dangerous for people passing by, airport vehicles and even small planes, and we must always maintain a huge distance to avoid receiving this jet.
So, is there any risk or damage to other similar sized aircraft queuing for takeoff or whatever?

Here you can clearly see the front one is turning. When they actually takes off, the waiting ones will either stay much farther behind or stay out of the blast.

The wake of a large aircraft can, of course, cause serious problems for another large aircraft following in the air;  American Airlines Flight 587 crashed because it flew into the wake of another aircraft and the first officer overreacted.

by "big planes", you mean "airliners", don't you? Technically the PerlanII is an Airbus and the X51 (even smaller) is a Boeing.

@MichaelSeifert that was wake turbulence, not jet blast

Worst-case scenario: Air Florida Flight 90...

@Sanchises you sure? That was when jet blast melted snow on the plane which then froze again on bad places. Then crew mistakes combined to crash the plane. Isn't there anything worse that could happen?

Hot air has been known to be ingested by the aircraft behind which can overheat engines and/or ECS leading to avionics cooling problems, particularly on hot days. In the case of avionics, there are thermal switches that will remove power before they get too hot and you will get a caution so it isn't really a risk as long as the pilot is monitoring their systems properly.

The airplanes in the photo are quite far apart, at least 1-2 lengths between each (it's just the long lens making them look cheek by jowl), and while in line going straight, they are only using a little over idle thrust to get rolling when required, so the jet blast effects are negligible.  The main factor is FOD (foreign object damage) kicked up, and at that distance that would mean sand/dust particles, but the effects of that would be too subtle to measure over the long term in any reasonably clean environment.
That being said, if I was in a desert area where there was drifting sand on the taxiway, I would probably increase my spacing a bit behind the guy ahead.  And you can bet that the guy in the (what looks to be a) King Air that is second in line in the pic - walking with the elephants - is keeping a little bit more distance from the elephant in front as well, owing to the size differential. If I was in the King Air I would be worried about the plane adding a big shot of thrust in both engines to start the turn (hopefully they'll just use the left engine), and the inside engine would be pointing straight at me part way through the turn, and I would be staying  well back.   Airmanship and all that...

You can seriously tell that's a King Air 2nd in line? Were you there??? That's some incredible plane spotting skillz!

The engine nacelle is a PT-6 so a King Air is the most likely candidate.

Wow, even zoomed in it's difficult to see that nacelle. #Impressed

There's no tail pipe out the back and you can make out one of the exhaust ducts just behind the prop.  PT6.

John, i also cannot say if it's really a King Air. It almost doesn't appear at picture '-'

Anyway, I edited my post to say "what looks like" to mollify the hyper-picky lol.


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How do single GA pilots prevent boredom during long flights?
My question somehow relates to this question asking about how pilots cope with boredom, but now the scenario is not the typical airliner configuaration with two pilots, but with only one. I'm thinking of single pilot operated business jets with flights over, say, 4 hours. What does the single pilot do to prevent boredom and associated problems such as vigilance loss and fatigue? They've got no one to chat with as stated in the first answer to above cited question... of course, they will continue to check and monitor systems, occasionally report and talk to ATC, but there is plenty of scientific evidence (i.e. see this book) a simple monitoring task can easily lead to fatigue - so are there any methods pilots use to prevent boredom and vigilance decrement?

While some business jets are certified single pilot, almost no business jet is operated with a single pilot (at least as a business-use jet, ferrying employees, etc), mostly for insurance purposes.

When I flew light singles and light twins commercially, we often had to have help unloading so we took turns with another pilot being PIC. We spent most the time betting on bazaar or the latest regulations - we kept score. The looser had to buy a couple rounds of beer at the end of the day. This was very beneficial - it kept us abreast of the latest regs. When I was alone, I played guessing games with myself; trying to see how close I could get to the correct time over the next fix, fuel calculations, testing the range of nav sites, how long I could go without touching the controls, etc.

Not long ago, I had my longest flight as a PPL: about 4 hours from Dallas, TX to Kansas City, MO, in a 172, facing a steady headwind the whole way, so making a ground speed of less than 90kts.
I ran checklists about twice as often as normal, and re-did my fuel calculations very regularly (in part because of the extremely slow progress).
I listened to the ATC frequency, and tried to build a good mental picture of all the planes around me.
I went through every single setting and option on my MFD glass cockpit and iPad.
I watched the scenery, both for visual navigation (despite my GPS), and just to admire the view.
Even after all this, the flight was pretty boring near the end, and I'm glad I don't do flights that long very often.

You have posted this answer on both this question and dupe question, don't you think it should only be on one?

This question got closed.   I posted my answer on the question that remains open.

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Why does Airbus continue with the A330-800neo despite only having 6 orders?
Airbus rolled out the first Airbus A330-800neo out of the paint shop last week (see press release).
Until now, this type has only six orders by one airline (U.S. Hawaiian Airlines, who switched orders from the A350-800 to the A330-800neo), with no new orders in the past months. According to various sources, even those six orders by Hawaiian seem to be questionable (see Hawaiian seeking A330-800neo alternatives).
Update 02/22/2018: The only customer, Hawaiian, has canceled their six orders.
Given these circumstances, why does Airbus continue to develop, produce and flight test the smallest A330neo variant? What is the business case for Airbus with one single customer?

Kuwait Airways has since ordered eight A330-800s, so Airbus once again has a customer for the -800.

There used to be a bit more demand. Hawaiian committed to 6 orders plus 6 options, and Transasia also ordered 4, coming to 16. Unfortunately, Transasia ceased operations and canceled their orders, and Hawaiian hasn't exercised any of their options yet. That leaves the -800neo at only 6 planes on order.
Update: Hawaiian Airlines announced they would cancel their orders for the A330-800neo and instead opt for the 787-9, signing a letter of intent to order 10 with purchase rights for 10 more.
Airbus was probably hoping for more orders and continuing development of the -800neo somewhat "at risk". Of the 1368 currently delivered A330ceo, 615 of them are the -200. This would suggest there may eventually be demand to replace those with the -800neo. Almost all of the A330 fleet is less than 20 years old at this point. There's still time for more orders as the A330neo only recently made its first flight.
As the first -800neo has now been built, most of the overhead in developing it has already been spent. There will of course be more as it must also be flight tested and certified, but evidently Airbus still sees value in going through with that. It will be a balance between Airbus recouping costs of development or avoiding costs of further development and support, and the needs of the customer.
Airbus probably also sees value in keeping Hawaiian happy. Hawaiian has not ordered any -900neos and they currently have 24 -200s in their fleet, suggesting that even if no other -200 operator orders the -800neo, Hawaiian might order more. Airbus may prefer that Hawaiian takes the only 6 -800neos they ever build than for them to go and order the 787 instead.
The 737-7 MAX is in a very similar situation. Boeing only has 58 orders for the type, which is 1.4% of the total orders for the MAX (the 6 -800neos account for 2.7% of the total A330neo orders). To compound this, the launch customer, Southwest, recently announced that they're delaying 23 of their 30 orders, possibly to covert them to a different version. Yet Boeing recently rolled out the first -7 and seems to plan on going ahead with it.
Since these planes have already been built, the manufacturers probably see some value in keeping the orders around so they can still sell the planes, and avoid the bad PR of going through the trouble to develop, sell, and build the plane only to cancel it. It remains to be seen if the airlines will continue to see value in taking delivery of types that no one seems to want.

I think you have to consider the future new-build freighter market.
If we assume that Airbus will have to convert the A330F into a A330Fneo, then the direct base airframe is the A330-800neo (since the A330F is a A332).
The other options are to either discontinue new build freighters (looks bad for customers), keep building one ceo model for the A330F (logistically hard), or use the -900 airframe (reduced capability for mass-limited flights).
There's a similar situation with the A330 MRTT, the tanker, as well.

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text:
How many aircraft does an ATC controller usually handle at the same time?
My question relates to the question What is the maximum number of planes a controller can control?, which asks about the maximum limit. One comment indicated 35 aircraft per hour for en-route segment. I, however, are not interested in the maximum number of aircraft per sector, but in the typical number of aircraft.
I am now interested in the typical amount of aircraft per enroute Air Traffic Controller at any given time during the day (how many aircraft are handled at the same time by an en-route controller).
While I am sure that there is no universal ground truth, can anyone report experience? To limit the scope, let's assume continental U.S. or Europe during the day, upper airspace.

Possible duplicate of How many aircraft can an ATCo control simultaneously, on procedural and radar service?

@SteliosAdamantidis: Not a dupe - that question asks about the maximum capacity, while this one asks about the typical number.

Depends entirely on complexity, rather than sheer numbers. In ATL I can comfortably handle somewhere around 60-70 departures per hour from a ground control position. More than double that when you factor in arrivals. That’s a VERY low complexity situation, with everyone moving one direction.
On the flip side, I’ve worked TRACON radar positions with five aircraft dodging severe weather and worked my ass off. High complexity.
ARTCC sectors are different in that they have known numbers, and will go from green to yellow to red depending on saturation. These are based on routings, in trail restrictions and so on. Again, all complexity.

I have had, at one time, 55 aircraft on my frequency, due to weather in Colorado, Kansas, and Wyoming forcing the early morning (5 AM local in Denver) eastbound rush over ONL VORTAC. Fortunately, controllers in other areas feeding my sector were looking out for me, and didn't send me any surprises. Thanks, guys.
Once I hit that peak, the push was pretty much over, and it dwindled down to 10 aircraft in about 15 minutes.
My airspace where the aircraft were concentrated is pretty big, though.
Normal traffic, during a daytime rush in that same airspace, would see 55 aircraft in half an hour, not at the same time.

While a very interesting anecdote, the question is about typical traffic volumes.

And, I answered that, as well.

Here in Germany we have sector Numbers in maximum of about 55 to 80 flights per hour- depending on the sector.
The live saturation is measured in 20 Minute blocks and a typical amount would be around 15-20 aircraft per 20 Minutes summing up to 45-60 per hour.

cool, thank you. May I ask which center in Germany you're talking of?

EDUU Karlsruhe @Stefan


text:
Does ATC react to pilot position reports?
Following previous questions on position reporting:

When do pilots have to submit position reports?
What are pilot position reports?

Does Air Traffic Control somehow react to pilots submitting position reports, are they acknowledged or even repeated by ATC?
What is the exact phraseology of such an acknowledgement / confirmation (voice, CPDLC, and ADS-C)?
Edit & Update: The background of this question is commercial oceanic operations. As pointed out in the answers, there are multiple different position reports. This question mainly focuses on oceanic position reports via voice & CPDLC.

I controlled non-radar airspace for about 2.5 years.
On your end, we’ll probably just say “roger.” We may add instructions to report a future point, or a control instruction.
On our end, we would be using that information for any required separation. For example, we may update a flight strip with your groundspeed, recalculate how we anticipate bring traffic across that same point, or change how we are protecting airspace or altitudes according to where you are. It varies depending on the environment and traffic, but the general concept is ATC is protecting the entire block from where we last knew you were - your previous position report or where you were last in radar contact - and your next reporting point. Your position report allows us to modify that protected area.
But little to none of that information will be relayed to the pilot, unless it is operationally necessary. Even then, it will probably just be in the form of a control instruction.

Note this answer is from a GA point of view

When you give a position report as a GA pilot in uncontrolled airspace, your transmission is acknowledged by ATC, often repeating back to you your actual position in the case of a Radar controller.
For example, a typical R/T conversation near where I fly may be as follows - this is typical of my first contact with an area Radar controller having changed onto frequency from my departure airport:

G-CD: Farnborough Radar North, Golf Alpha Bravo Charlie Delta, Request Traffic Service
  FR: Golf Charlie Delta, Pass your message
  G-CD: Golf Charlie Delta PA28 2 POB VFR, Routing Elstree to Turweston, 2200 feet 1016 London QNH. Currently abeam Bovingdon heading 270
  FR: Golf Charlie Delta Sqwark 5020 QNH 1017 Radar contact 2 Miles East of Chesham, Traffic Service
  G-CD: Sqwark 5020 1017 QNH

Note the emphasised section. I had given an approximate position to the controller to allow them to identify me. They have used that information along with my transponder code to exactly identify me on their screen, and read back to me my exact location.


text:
Why do propellers have a specified range of diameters, with both maximum and minimum limits?
I want to know what exactly the minimum and maximum diameter means in a prop. For example, in a Cessna 152, we have a McCauley prop with a minimum diameter of 67.5 inches and a maximum diameter of 69 inches. For reference, the propeller model number is 1A103/TCM6958.
I'm having some trouble understanding what exactly this range means. Is it related to the expansion of the prop due to heat? For example, it has a diameter of 67.5 inches when cold and expands to 69 inches when hot?

The prop is 69 inches when new.  Longer and it would probably hit the ground or other issues.
As the aircraft is used, it may get nicks in the prop.  These are most likely to happen near the tip.  A certificated mechanic is allowed to blend things like that out.  If one side ends up shortened, they need to do the same to the other side to keep it mass and aerodynamically balanced.
In the end, the 67.5 is a maximum limit on how much the prop can be shortened through its life of maintenance activities.

Usually the aircraft / engine / propeller is certificated as a unit.  The performance numbers in the flight manual etc. are all specific to that combination.
There can be STC's for other props -- or revisions, etc.  Just like for alternate engines.  However, those usually will come with a different flight manual.  Those also probably also have different max / min limits on the prop diameter.
The 69 in 1A103/TCM6958 probably means 69" diameter and the 58 probably means 58" of pitch.

It may seem odd to have a limit on how much can be removed, but there must be some limit.  If a propeller is in service for 30 or 50 years, then a mechanic working on it needs to know 'how much is too much'.

@MichaelHall I agree that the flight manual performance numbers will have some margin in them that are good to the 67.5 diameter -- but that the company doesn't want to promise anything about a prop trimmed to 65".  When you suggested a 68" prop, I thought you were talking about a different part number with a nominal 68" diameter -- a different design, possibly from a different manufacturer.

A different part number needs an STC and potentially revisions to the flight manual.  Take two 69" props - one a 'cruise' prop and the other a 'climb' prop. They'll differ in takeoff distance, rate of climb, cruise speed, and fuel economy at cruise. The airplane manufacturer won't give allowance for "any propeller between 67.5 and 69 inches diameter". Of course, company B might want to offer a bolt-on equivalent to company A's propeller. In that case, their two 69" offerings may have nearly identical performance - but it would still be certificated separately and require an STC proving safety.

got it, thx.  deleting comments ...

A mechanic in the field will not remove material from a tip that shortens the blade beyond some light dressing that his no noticeable effect visually. 99% of dressing is on the blade's leading edge. When I dress out my prop I'll count the file strokes and try to duplicate the action on the other blade.

They may have a tight range on fixed pitch props due to engine loading factors.
The tip of a 69 inch propeller at 2400 rpm will move at:
2400 rpm × $\pi$ × 69 inches × 1 mile/5280 feet × 1 foot/12 inches × 60 minutes/hour = 492 mph
The extra inch and a half on the end will produce considerably more thrust at a given rpm.  The shorter one will need higher rpm for the same performance.
Higher rpm shortens engine life.  For an aircraft on a regular maintenance schedule, deviation from specified engine loading may not be safe.

The 67.5 inches is the shortest a propeller shop can make the blades if they have to remove damage, say from a minor tip strike or a fatigue crack detected during an inspection.
Mechanics in the field will generally only dress out blade leading edges due to nicks and dings. They won't remove material from a tip because specialised processes and tooling is required to have the reworked blades identical and in balance.  If a tip itself gets damaged or bent or has a crack, the prop will go into a certified shop.
The minimum length specification means the shop can remove up to 3/4 inches off each tip to remove the damaged metal and make the prop airworthy again (while doing that, they may repitch it slightly, twist it coarser, to compensate for the lost blade area in order to get the same static RPM when running the engine on the ground). If any more material than that has to be removed, the propeller is ready for its new life as a clock.


text:
How does momentum thrust mechanically act on combustion chambers and nozzles in a jet propulsion?
I'm asking this question since I can't intuitively understand how the acceleration of  mass flow and therefore the increase of its momentum can actually mechanically act on the combustion chamber walls and nozzle walls to induce momentum thrust.
For example, when it comes to pressure thrust induced by pressure recovery at various diffuser sections within a propulsion system, it is easy to understand that the parallel component of the force (parallel to the axis of total thrust vector) acting on the diffuser walls of the inlet, compressor diffuser, compressor stator blades, etc will induce an asymmetric load and therefore result in forward thrust. It is also intuitively understandable how the propeller/fan/compressor of gas turbine engines will induce thrust, since it is mechanically altering the mass flow, giving it more momentum and as a result of conservation of momentum, an opposing momentum, i.e. momentum thrust will occur on the individual propeller/fan/compressor blade.
Though, how does the reaction force actually act on combustion chamber/afterburner or nozzle walls? For example, from what I understand the combustion chamber and the afterburner of the gas turbine engine is a constant pressure device so it's not an increase in pressure load acting on the engine compartment that is resulting in thrust when it comes to combustion chambers of gas turbines. The way I understand combustion is that it adds heat energy to the mass flow, and subsequently some of that energy will do work and get converted into kinetic energy resulting in increased mass flow velocity. I can understand that somehow, the expanded gas would be interacting with the chamber wall mechanically resulting in increase of momentum and reactionary force, but it's just not intuitive enough and I'd like to have some better explanation to it.
As for the nozzle, according to NASA's beginner's guide to aeronautics nozzle is not doing any thermodynamic work and there's no pressure change throughout the nozzle. Though this seems a bit counterintuitive to me since my understanding is that a nozzle decreases the pressure of mass flow and increases its velocity. For such reason it is also not understandable to me how the nozzle exit speed greatly influences total thrust when there is no thermodynamic work involved (i.e. conversion of thermal energy into kinetic work, increasing momentum); it must mean that I'm not understanding some basic fundamentals correctly.

Welcome to Aviation.SE.  Interesting question, and something that I didn't realize I don't have an explanation for, until I see it asked like that.  Nicely done!

@RalphJ Thank you. I've been searching for the answer of this question but came to no avail through quite a few literatures. It is somewhat counterintuitive to me so hopefully I can get some answers!

Related: On which point(s) in a jet engine does the reaction force act?

@sophit Yes, thank you, this is exactly the answer I was looking for. So would it be correct if I think of shear force (action) induced thrust (reaction) interacting with combustion chamber rigid body in the same way how a boundary layer induces drag through shear, but reveresed?

It all comes down to where you draw your control volume.
At one extreme you can draw your control volume as a simple rectangle box 'around' the engine, but with a good bit of space between the boundary of the volume and the engine.  The 'top' and 'bottom' boundaries of the control volume are streamlines -- no mass flows through them.  The 'front' of the control volume is the inflow -- it is far enough ahead of the engine that flow entering the control volume has freestream properties.  The 'back' of the control volume is the outflow.  It has two portions -- the flow that went around the engine (the boundary is far enough away that this again has freestream properties) -- and the flow that went through the engine.
With this control volume, all of the control volume boundaries have equal pressure on both sides, so there is no pressure contribution to thrust.  However, the flow that goes through the engine has a change in momentum, which leaves us with $T=\dot{m}\,\left(V_j-V_\inf\right)$.
Where $V_j$ is the jet velocity, $T$ is thrust, $\dot{m}$ is the mass flow through the engine.
At another extreme, you could shrink the control volume down such that it coincides with all of the surfaces of the engine.  In this case, the only mass flow that crosses the boundary is the fuel flow coming in from the injectors.  If they point aft, they will contribute some thrust, but they could also be arranged to contribute nothing to thrust.  To obtain the thrust, you need to perform a detailed integration of all shear and pressure forces on the boundary on every surface.  These surfaces point in complex directions, so to do this integral, you have to be really careful.
Both of these approaches (and any in-between) will give the same answer.  Every action has an equal and opposite reaction.  Things that happen entirely 'inside' the control volume can be ignored -- they cancel themselves out such that all we need to worry about is what happens to the control volume boundary.
In practice, it is much simpler to draw the control volume far away.  It makes all the math & bookkeeping much easier.  It gets us the overall answer -- but without a ton of details (what is the force on an individual compressor blade).
What matters is consistency.  You can't draw your control volume one place -- and then try to reconcile that part of the boundary with something that happens on the interior of the control volume.
This also works in the opposite manner.  Instead of a control volume, you can think about a control mass -- a small chunk of fluid moving through an engine.  We can think of it as a tiny cube.  It starts off with freestream properties.  The only forces that act on this control mass are pressures and shear on the six faces.  The control mass will accelerate due to these forces.  The energy of the control mass can change due to heat transfer in or out of each face.  If the control mass is up against a boundary, then the pressure on that face will equal the pressure on the boundary.
The acceleration of the flow is intimately tied to the pressures in the flow and on the surfaces that interact with the flow.
In a simple model of a rocket, the combustion chamber is at constant pressure, but that is certainly not true in the nozzle.  The nozzle expands the flow and accelerates it.  Fundamentally the nozzle converts the thermodynamic energy from combustion into kinetic energy of the exhaust gas.  As it does this, the gasses expand from high pressure in the combustion chamber to ambient pressure at the nozzle exit.  A jet engine adds a turbine between the combustor and nozzle in order to extract work to drive the compressor (and anything else).  But the turbine is also a flow expander (like the nozzle).

Thank you for a thorough answer regarding the methodology. In answering my question I think setting a control volume that has boundaries that matches exactly with engine surfaces, as you've suggested, would be most helpful. Also, you greatly helped by suggesting that I should look into shear; I've considered that shear in this case would probably only contribute to the rearward thrust for some reason, although I'm probably wrong with that assumption.

I'm glad I've reminded you about shear -- but it isn't a significant player in propulsion. In fact, it will almost always amount to a loss (source of inefficiency). Most propulsion analysis can be done in terms of quasi 1D flow -- where there is only one component of velocity (x), but the cross sectional area can change (A). When doing Quasi 1D analysis by hand, we usually work from station to station -- engine inlet, compressor face/exit, burner inlet/exit, turbine inlet/exit, engine nozzle, etc. By hand, we don't pay close attention to the details of the area change between stations.

However, Quasi 1D can also be applied in much more detail, breaking each engine component into many steps and then subjected to numerical methods.  In either case, F=P dA.  Force is pressure acting on the change in area.  The force on the air is equal and opposite the force on the walls of the tube.

Oh, so does that mean you could disregard of mass flow itself and just calculate using given pressure and rate of area change subject to pressure at any given part of the engince? Also, what you've described about shear is how I've also initially understood, that shear caused at boundary layer at the surface of each engine components would lead to surface drag. Though after reading your post and comment from Sophit above, I've thought that maybe shear is how momentum thrust is derived, especially in isobaric process where there is no area change. Am I understanding this wrongly?

If you knew the pressure everywhere in an engine, you could calculate thrust by integrating pressures (and you would need to know the fuel flow rate to the injectors).  This is the idea of the 'shrunk down' control volume approach.  The shears are there, but they are a viscous effect that always act against motion - they are not essential to making thrust.  With the shrunken control volume, there is no fluid in the control volume -- so there is no air to accelerate.  We ignore it.  With the big control volume, there are no surfaces for pressure to act on, so we ignore them.

Equal and opposite reactions -- the pressures on the surface of the engine (pressure thrust) act to accelerate the flow through the engine (momentum thrust).  They're the same thing.

Thank you very much for all your effort in trying to help me understand all this Rob. Much appreciated.

how does the reaction force actually act on combustion chamber/afterburner or nozzle walls?

Let's first clarify what the reaction force is: It is the force which accelerates a mass of burning fuel-air mixture while it passes through the combustion chamber.
What causes this acceleration? In Newtonian physics, a force is needed to accelerate a mass. Here, acceleration happens due to the isobaric heating which expands the burning fuel-air mixture. In an isochoric process (volume stays constant), no acceleration occurs but pressure rises. Here, the burner can is open at both ends and surrounded by colder air, so the volume of the burning fuel-air mixture is free to expand in all directions. However, there is high-pressure air flowing in from the diffusor which blocks the expansion in forward direction and to the sides. However, downstream expansion is still possible, so that is where the gas expands to, accelerating in the process.
In one sentence, the force which accelerates the gas in the combustion chamber is the pressure force of the air flowing in from the compressor and diffusor.
To be precise: The flow in the combustion chamber can best be approximated as a subsonic Rayleigh flow, so a small pressure loss can be observed along the flow direction as the burning fuel-air mixture heats up and its stagnation pressure drops along the way. Also, friction will cause another pressure loss.

Thank you so much. I've realized talking with another person that I was too focused in the word "constant pressure" (or as you point out that combustion in a constant diameter combustion chamber is isobaric) and ignored the fact that pressure drop at turbine inlet nozzle would naturally induce the mass flow to a rearward direction. As for the other part of the question, I think Sophit and Rob gave me the answer, that shear forces could act as an action force that results in forward acceleration of engine rigid body from reaction force. These two clarifications answer the question I've asked.

@MK.s I wouldn't put so much importance on shear. Pressure is the dominant source of the propulsive force. By far.

From a fluid dynamics point of view, forces can be transmitted either through pressure or viscosity (aka friction aka shear).
The pressure contribution is by far the biggest one and can be simply understood by looking at the following picture (taken from this answer):

This picture is about the combustion chamber of a rocket, but the basic idea is the same: the horizontal force is given by the pressure acting on all the vertical areas of the chamber. As pointed out in another answer, the combustion in a turbojet/turbofan happens at more or less constant pressure so that the biggest contribution come from the vertical end of the combustion chamber and of the nozzle.

Thanks for the answer, though my question would then be how an afterburner works. As you'd know the afterburner fuel injector/flamholder is separated from the turbine exit diffuser cone and afterburners also "doesn't apply additional pressure forward of the fuel injector". Shouldn't that mean there is no "plane that is normal to the nozzle axis" where the thermodynamic work of the afterburner can act on? Or is it that, although there is no pressure increase within the afterburner chamber, additional force is still being transmitted to the diffuser cone?


text:
How to find runway Centerline spacing on airport diagrams?
I know that airport diagrams show the exact position of airport runways in DMS (degrees, minutes, seconds) and therefore could use trigonometry to find how far apart runway centerlines are from adjacent parallels, but is there a more accurate way to find runway centerline spacing on these diagrams?

How accurate do you want to be? Do you know the accuracy of the published data?

Here is the airport diagram for Denver International Airport, which has numerous parallel runways.  I don't see any scale that could be used to measure distances.  Looks to me that one would have to do some math based on the latitude/longitude information provided, and which is provided here so no interpolation is needed:  https://www.airnav.com/airport/KDEN

You could take the known lengths of the runways to determine scale

The scale is usually depicted on the chart. Just take a ruler and measure.

Good idea. I could measure any of the runways on CrossRoads's KDEN diagram to get 12000 ft. and then extrapolate to get the measurements I want!


text:
Is there a age limit to become a CFI?
I’m a new PPL and I would love to become a CFI in the next 2 years (or so). My objective would be to transfer what I know (and will have learned) to aspiring pilots. I’m older, though (just about to turn 60). Put it bluntly: am I too old? I know that we can’t talk about people being too old for almost anything these days, but I really would like to know if anyone (e.g. a flight school) would hire an instructor who not only brings rather thin experience (300-400 hrs by then) but combines it with rather ‘advanced age’. The benefit for a school would be that this would be my ‘forever-job’ (first, part-time and then full-time after I retire from my ‘day-job’ in a few years), not a stepping stone to an airline career. Please, feel free to tell me what you really think…

A flight school won't care too much about your age if you have the required medical.  And mentally, your age is an overall plus since a flight school would generally prefer a mature individual in it because they want to teach to a 25 year old who's just building time.  The turnover with flight schools is quite high so the prospect of getting say at least 5 years out of you is another plus because they may be only getting 2-3 years out of younger instructors in the current environment (often they are basically only hanging on to get to 1500 hours under the "Colgan Rule" craziness).
I would say that that if your health is fine and shows no signs of problems over the next 5 years at least, you should definitely go for it.  You might even get a school to commit to hiring you, or at least giving you a shot (it's going to come down to how good a teacher you are), if you train with them.
With the general shortage of bodies all through the system, I don't see any downside if you really keen on doing it.  If you gain a reputation as a good teacher students will gravitate to you over the youngsters.

A CFI only needs Basic Med or a Class III to instruct. Why do you think a flight school would require more than that from an older instructor?

Ooops I'm in Canada where you need a Cat 1 because the instructor rating goes on top of a commercial license and that requires Cat 1.   Post fixed.

In the US you also need a Commercial Certificate to become a CFI. You only need a Second Class medical if you want to exercise Commercial privileges. Instructing requires a Third Class medical—which for someone over 40 is every 24 months. An exam every 6 months is only required for ATP pilots over the age of 40. Every 6 months seems a bit much for an instructor.

In Can a class 2 medical only applies to Controllers.  All Comm is Cat 1 all the way up the chain, and private is Cat 3, and there is also what is called Recreational Pilot which is self certify which is more or less a PPL restricted to 1 pax and day only.

Age is no barrier to becoming a CFI.  You bring a lifetime of experiences that you can use to teach and mentor new pilots.  Some of my best instructors that I have ever had were in retirement age.  They generally took more time to correct deficiencies and were more patient.  They weren't concerned with external pressures at home or looking to sit right seat in the multi engine King Air across the ramp.
If you ever lost your medical you can still teach ground school classes, sim sessions and still flight instruct in aircraft provided you are flying with a client who can be the legal pilot in command (i.e. no private or instrument students or expired flight reviews).
There is no requirement in the FAR §61.23 for instructors to hold a medical certificate with the exception of also acting as a required crew member or legal pilot in command.

Absolutely not.  If you love flying airplanes and love to teach others how to fly, we need more CFIs like you.  These days you can practically pull out a sectional chart and toss a pub dart at it, and whatever airport the dart lands next to, you can probably get a flight instructor job out there.  Keep in mind the pay is not very glamorous until you get a couple thousand hours of instruction time under your belt.  Some schools may want you to hold an instrument rating on your flight instructor certificate so you can do instrument training.  The only real obstacle would be maintaining a medical certificate if you intend to do primary and instrument flight instruction.  Aside from that, no there aren’t any age restrictions and it can be a very rewarding side job if you’re so inclined.

There is no upper limit on age for a CFI.
A medical is necessary for primary instruction where the student is not rated.
A medical is necessary for instrument instruction, as the instructor must act as PIC for the safety of the flight.
A medical is necessary to perform flight reviews and IPCs as each requires flight solely by reference to instruments, by the applicant.
One can obtain a CFI with a third class medical, and the local FSDO has provided CFI initial rides to applicants with only a third class medical.
14 CFR 61.39 (a) (4)
(4) Hold at least a third-class medical certificate, if a medical certificate is required;
The above requirement may be defacto amended by the Basic Medical rules, where the aircraft to be flown is compliant with Basic Med requirements.
While I have heard stories of ATP rides in Level D simulators, without medicals, I do not have first hand knowledge of any cases.  IMO likely possible, because a medical is not required.
Other ratings may be accomplished if the DPE is willing to act as PIC for the flight, and I know of one example of that.
A third class medical will be sufficient for instruction. A Basic Medical may also be used with many common general aviation training aircraft.
But as for the age limit on CFI, there is only a lower limit, which you have long since blown through. I would suggest that you consider a AGI and IGI ground instructor certificate, which you can work on immediately.  Good luck and have fun!


text:
Is there a good reason to have a handheld Aviation Microphone in GA?
I have a Cessna 172P in which the handheld microphone has stopped working. Before I replace, I was wondering if there is any good reason to even have one? I have PTTs on both the pilot and copilot, yoke.

Have you ever used it? I've only seen an instructor use it once, when the radio jack failed for the mic input.

Have used it once in the last 20 years when I didn't have my headset with me.

They are not incredibly expensive, I wouldn't have it high on the priority list, but you can replace it if you want. It is an owner-replaceable part since it just plugs into a jack, you shouldn't need an avionics department (and bill) unless you need to pull your panel apart to get to it.

I used mine a bunch.  It's nice to have if your ptt breaks.

According to the 172 Minimum Equipment List from Cessna (S and R models)

these are both Category C items which the MEL states

Category C: Items in this category shall be rectified within ten (10) calendar
  days, excluding the day of discovery.

So it looks like you may need to fix it but in the event you are flying it looks like you need an alternative (headset should do that) and or a backup headset on hand.
However the 4th column states that zero are required for dispatch so you can fly without it.
As people are noting in the comments in a lot of planes these mic's go more or less unused or are inop these days. I know I have never personally used one in any of the archers I have flown.

That's for a commercial operation.

Still a category C

Ask yourself the question; you call tower to respond to an instruction or something, and there is no response, or tower starts calling you because they haven't heard from you even though you thought you'd talked to them, and you need some kind of standby device right now to talk with without having to fumble around.  Be nice to be able to grab a mic that normally just sits there unused.
Maybe you have a spare headset on board, but imagine having to fumble around to get it out and plug it in while your attention is needed elsewhere.
So if you have a spare headset plugged in and ready to go that you can grab without much effort and use, not a big deal, but if that's not the case and you fly in controlled airspace a lot, I would say you should have one.

I have the number for local ATC saved in my phone for this purpose

What about "not local" ATC?


text:
How changes in Air masses, Air flow direction and intensity affect lift?
I have a question regarding the airflow an aircraft experiences during 3 distinct scenarios:

An aircraft during landing, experiencing a sudden gust of 40 knots from the tail. What would be the immediate consequance- Airspeed, lift?
All this if the aircraft does not correct the situation with pitch/ engine thrust.
An airliner cruising at 270 IAS, suddenly experiencing into an area of tailwind- meaning- the tailwind component of the wind aloft changed and increased by 40 knots. How would the airspeed look- just the following moment, and from there- lift? Regard to the situation without any compensating action by the pilot,
A fighter jet, at 20,000 feet, turning from at 25 degrees per second, meaning doing 90 degrees in under 4 seconds, from a situation of 50 knots headwind to no headwind. If the air mass is stable and blowing at a constant 50 knots, would there be any change in the characteristics of flight to the jet, meaning deteriorating airspeed which he/she would have to compensate for using pitch/thrust adjustment? In this situation, we assume that the pilot doesn't care for maintaining ground speed or track, just keeping the turn at a constant rate of 25 degrees per second.

My question is (and we discussed it in the previous question)- is there any diminishing effect to the fast change of airflow that was just ahead and changed to sideways/behind- when the change is caused by the aircraft itself, just as witnessed (by me recently) in an airliner when suddenly encountering a different air mass (I witnessed increasing Ground speed but decreasing IAS, until the Autothroottles commanded a slight increase in thurst).

Could you elaborate on the context of your question? I hope we are not doing your homework.

I already understood the problem, as written here:
link

Related and we have a number of other questions about sudden changes in wind direction that might be helpful.

Re case 3, it might be more instructive to consider the case of a hang glider circling at 30 degrees per second, flying at an airspeed of 20 mph, in the presence of a 25 mph wind.  What do you think the glider "feels" in terms of a tendency to pitch up or or down, or to lift up or drop, or in terms of any tendency for the airspeed to change?  Do you understand why?  Likewise do you understand why the "dynamic soaring" technique of the albatross is entirely dependent upon the presence of a  vertical wind gradient (+ an extra boost from slope lift effects)?  It cannot work in a uniform airmass.

For sake of simplicity, lets state that lift is produced by airflow over and under the wings (the rest of the airframe also contributes, but in the scope of this question we can neglect that).
Lift for any given airfoil is basically dependent on airspeed and angle of attack. Up to a certain limit any increase in airspeed or angle of attack will amount to increasing lift and vice versa. So, the question:
Case 1. and 2. The situation is the same. Sudden tailwind of 40kts will lead to a sudden 40kt drop of airspeed and sudden decrease of lift. The groundspeed will start to increase (slowly, because of inertia of the plane). If immediate corrective action is not taken, some altitude will be lost. Near the ground this would be catastrophic.
Case 3. I'm a assuming a level turn here: During or after the turn the wind will not have any effect on the airspeed or lift of the aircraft.
The aircraft is flying embedded in an airmass. If we are considering aerodynamics (lift and stuff), all changes made in the flightpath of the plane are made in relation to the airmass. Not the wind, not the ground. The wind is simply the movement of the airmass in relation to the ground.
If the wind does not change, nothing changes for the plane (overly simplified, of course, there's temp, pressure etc, but that's not on subject here). In cases 1 and 2, the wind changes, as the velocity is momentarily different (gust). In case 3 there is no change in the wind.
Your example of the event you've witnessed, with increasing groundspeed and decreasing airspeed is a simple case of flying into a region of tailwind. Tailwind would simultaneously reduce your airspeed and push you to go faster in relation to the ground, increasing your groundspeed. This event might happen as a result of flying somewhat perpendicularily through top or bottom part of a jetstream.
Since this subject has proven to be somewhat difficult to comprehend (here and in this question too), let us end this answer in a humouresque article on Flying Magazine website, that might help understand the misconception of turning in wind: The Last Word on Downwind Turns, Really.
As a sidenote, in case 3 you have described a rather steep turn without increase in engine power, the aircraft will bleed energy during the turn resulting in loss of airspeed, if airspeed is not maintained with power or glide. I'm also pretty sure that a constant 25°/second rate of turn is just too much to sustain for most fighters, even with full afterburners, and it is definitely too much for any pilot to handle for long. F-16 has a max rate of turn of about 27°/sec at about 380kts and 9g's.

For your answer no.2- regarding the Jet fighter- yes, a level turn, without bleeding airspeed (assume engine was added prior to the beginning of the turn).
And still, I am having a difficulty understanding why these examples are different., just due to the reason that the jet self- positioned itself into a "different air mass, in contrary to the airliner which accidentally flew directly into it.
What I can say for sure is that probably due to the immense force and overpower of the fighter,  with some more engine power/slight change in pitch- the wind change goes unnoticeable.

But the wind does not change...

I edited the answer a bit, maybe now it's more clear?

as per your last note about the F16- yes it's about that.
but it's no problem to maintain a turn at say 15,000 but I did exaggerate a bit.
We can point it at 15 degrees per second, making it 6 seconds, as seen here-
link.
I agree with most of you answer, except the last part-
If the fighter jet turns 90 degrees in 6 seconds- meaning losing a headwind component, it changes the wind for himself, by turning it by 90 degrees.
Now the question is- is a wind change is also self made.

There is no wind change.

I think what I am trying to say is that a fast turning aircraft- just as a helicopter- changes it's own airmass in which it works. just as when a helicopter or a slow moving aircraft turns form head wind to tailwind- it experiences momentary changes of airspeed indication do to the abrupt change of wind direction.
And as I was looking for good reference, I found the complete opositie :)- link.

And another one.. Planes make the theory of relativity be a little on the egde there, due to their mass and characteristics. Hard to grasp!
Here is the second link, tell me what you think! link

I'm thinkin' that if those articles are saying the wind does not change during turn as a result of the turn, they are right.

I understood something while walking to buy cigarettes now, thinking about one of those articles. I will post the answer in a second.

As mentioned in Why do gusts change the airspeed during landing, but turning (which changes where the wind is coming from) does not?

The immediate effect will be a loss in airspeed and lift. Groundspeed will stay the same. The aerodynamic forces of thrust and drag will catch up causing the airspeed and vertical speed to return and the groundspeed to increase.   If not recognized, this could be a dangerous situation. A sustained tailwind will cause your landing to be long and flat. You will be moving along the ground at a greater rate than desired unless you reduce thrust and airspeed. Since you can only reduce airspeed so much, alternatively, you can increase vertical speed in your descent rate to maintain your 3-4° glideslope. Either way, you have to watch your horizontal (ground) speed, ground roll, and Landing Distance Available to not overshoot the runway nor float due to the reduction in wind velocity near the surface caused by surface friction with the ground. Because of this, a 40 knot gust factor or tail wind may be too much for most GA airplanes.
In an airliner flying at cruise altitude and speed would not be affected by the change in wind velocity. In cruise, the gust factor is a smaller percentage of speed than it would be when landing. The instruments would indicate a momentary loss of airspeed and an increase in groundspeed and negative (downward) vertical speed. This may go unnoticed by the pilots, because it will happen and recover quickly unless the change is sustained. It will instead be experienced as turbulence.
The practical effect on the fighter jet would depend on  its airspeed and thrust. That quick of a turn would require a lot of bank. If constant bank were maintained in a level turn at constant thrust, the aircraft’s airspeed would remain constant. But, it’s ground track would not remain constant. The airplane would drift downwind. The slower the airspeed, the more the aircraft would drift off of its constant radius. The faster the airspeed, the less apparent the drift. The ground speed would be determined by the aircraft’s heading in relation to the wind vector.

Ok, I was wrong.
In order to better understand what is happening, other than saying that the plane flies embedded in air mass, it is easier to understand that the turn, no matter how fast it is- maintains equilibrium. meaning- it is not abrupt in no time, but a collection and a gradual turn into the tailwind or vice versa.
This is easier understood by looking at each particle of air in which the jet fighter is flying. every second millisecond etc.- that the plane turns, the particles travel with it by the same velocity in relation to the ground, making it move altogether.
The situation would be different it the aircraft turn 90 degrees in no time, making the air around it change direction in no time- like happens in a windshear or inversion.
Whooa that was interesting!

Close but no cigar. In the event of a sudden (infinite g), the wind would still not be a contributing factor. Please read the article I linked in my answer and try what is described there out yourself, on your next flight for example.

I want to correct myself- If we changed our vector completely to a different direction, meaning basically beaming 90 degrees to the right- then- we would experience a sudden change in airspeed.

And i couldn't spot your link.

This: https://www.flyingmag.com/pilots-places/pilots-adventures-more/last-word-downwind-turns-really/

AHH that i saw,,

When testing the theory in the article on the aisle of your aircraft, try to look professional not to scare the passenger and/or crew.

I will hold a note with your name of course :)


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What are the disadvantages of fitting underwing flaps to a Mirage III/5 fighter jets to lower landing speeds?
The Mirage III / 5 series of fighter aircraft are versatile aircraft, but has a high approach speed of 180 knots and a high landing speed, requiring long runways.
Underwing flaps, like those of the Gloster Javelin, would surely work, and the fact that they are close to the CG would not cause an acceptable pitching moment. The tailless swept wing Messerschmitt P.1111 also had flaps on its trailing edge.
Gloster Javelin in landing configuration
Tested on a small free flight glider, I found that the flaps on a delta resulted in a noticeable increase in lift and decrease in turning radius, the elevons were not overwhelmed by the downward moment of the flaps. Using trailing edge flaps on a the same delta wing model resulted in an unacceptable downward pitch that could not be counteracted by the remaining set of elevons.
I would think the system would work, however my question is what sort of performance effects: increase in weight, for example, and possibly drag, would result.
Later models of Mirage incorporated canards and other devices to reduce landing speed did Dassault Aviation overlooked this option or did they evaluate it and decide that it would not be worth it?
I would have incorporated these in any delta wing fighter I designed, at least to offer it as an option to customers like the tailor made canards were to be offered.

You talk of underwing flaps, trailing edge flaps and simply of flaps. Can you clarify these distinctions, as you are not using the conventional terminology.

For a pure delta, anything that changes lift distribution affects attitude. I don't think they actually wanted to redesign and decouple that. The canards are more like vertex generators while the attitude control is still on the flaps.

"...did Dassault Aviation overlooked this option or did they evaluate it and decide that it would not be worth it?"  Please don't take this the wrong way, but I think it would be a little naive to presume you may have hit on a solution that a team of their best engineers failed to consider.  Also, unless someone here was a member of that team the best you can hope for is speculation.

Every airplane is a compromise of conflicting demands. While I am not intimately familiar with the Mirage family, I can easily see why flaps were never included.
In the early Fifties when work on deltas started at Dassault, the most important design parameter was top speed. High landing speeds were accepted, and given the design alternatives to a delta (think F-104), the landing speed could be considered low and another plus on the side of deltas.
When the first Mirage III were ordered, they had to serve in four different missions: As an advanced trainer (Mirage III B), an interceptor (Mirage III C), attack aircraft (Mirage III D and E) and for reconnaissance (Mirage III R). In order to allow for the widest variation in external loads, the lower wing should be free of flaps or other equipment which would restrict the attachment of tanks, armament or reconnaissance pods. Mounting any flaps at the straight trailing edge would require an opposite deflection of the elevons, negating any lift gain.
Flaps on naturally stable tailless aircraft are only helping if they are attached at a point ahead of the pitch trim flaps. This is possible with swept wings (see the Horten IX glider with its small flaps below) or with split flaps at mid-chord, like on the Gloster Javelin. With a straight trailing edge, no lift increase with a naturally stable configuration will be possible since the additional pitch moment of those flaps must be compensated at the same lengthwise location by the pitch control surfaces. What is gained with the flaps must be destroyed for pitch trim.

Horten IX V1 in tow, flaps lowered (picture source)
Since the Mirage line was never considered for use with aircraft carriers, its landing speed was accepted as part of the overall package. The Gloster Javelin was designed as a pure interceptor which put fewer demands on its lower wing. Also, the Javelin's tail helps to trim the aircraft in the landing configuration.
From the US translation of "Aerodynamique de la Nouvelle Generation d'
Avions de Combat a Aile Delta", published in the AGARD Conference Proceedings No. 241:

Its [the Mirage III] aerodynamic formula, a delta wing swept back 60° at the leading edge, allowed Mach-2 flight with a single engine of 6 tonnes thrust, while its competitors were equipped with a 7-tonne J79.
The trade-off to this supersonic performance was a large increase
in the approach speed, 180 knots instead of 140 kt for the Mystere family. This constraint was accepted for the Mirage III, but later program specifications from the General Staff of the French Air Force required an approach speed below 150 kt.

So the Mirage III users had second thoughts, after all. The result of this lower approach speed requirement became the Mirage F-1.
Note that artificial stability allows to lower trailing edge flaps on a delta wing; the Mirage 2000 could be flown down to 100 kts airspeed.

"Tested on a small free flight glider" gets a +1, but here some book knowledge helps.
At lower Reynolds numbers, the classic airfoil shape looks good, but most lift comes from the bottom.  This is why insects have flat wings and birds have delta tails and heavily undercambered wings.
Flaps work very well on straight winged aircraft at higher Reynolds numbers because they improve both bottom "pressure" lift and top "Bernoulli" lift by increasing camber, much more so by combining them with slats, and particularly at higher aspect ratios.
But flaps help a lot less with low aspect deltas, slats a bit more.  Some lift enhancing devices were proposed for the next generation Concorde, but one need only build a longer runway (and strong tires) for the original to work fine.
For lift vs drag efficiency, top lift generated by airflow over a cambered surface is by far the best until Mach effects (approaching transsonic speeds) begin to cause an increase in drag.
Then, it's back to the bottom again for less efficient lift production.
The advantage of deltas, early in the supersonic age, is they were very stable and used vortex flow over a swept leading edge, along with bottom "pressure" for lift.  Rockets with low aspect delta fins were routinely breaking the "sound barrier" 10 years earlier than the straight winged Bell XS-1, and the thin winged lower aspect Spitfire came close (before losing its prop).
So, while deltas make very graceful paper airplanes, the much higher wing loading at full scale (weight/area ratio) makes them rather brick like at lower speeds.  Especially for military aircraft, one would go with the longer runway, or, like the Swedish Viggen, use vortex enhancing canards to improve short field performance.

Another answer that gives yet another factor for why it probably wasn't done: it's not necessary for delta wings.
One of the limitations you have in exploring the flight envelope of delta wings is that you have no active control over a free-flight glider: you cannot alter the characteristics in flight. If you have experience with RC planes you will notice another characteristic of delta wings: flaring the wing dramatically increases both lift and drag.
In effect the entire delta wing is it's own flap. Unlike narrow chord wings (straight or swept) one of the interesting characteristic of delta wings is that they can maintain effectiveness of elevon control at very-very high angle of attack. In fact, way past what would normally be considered its stall point.
There have in fact been delta wing planes that use flaring as analog of deploying flaps: both the Concorde and the Tu-144 were designed with nose cones that drop so that pilots can see the runway on landing approach while the entire wing flares.
I suggest you perform another experiment with your free-flight glider. Instead of adding flaps increase the elevator action of your elevons and see how much more lift you get from it.
The Mirage however was not designed with a droppable nose but pilots still used the flaring maneuver to slow down on landing. Perhaps being a military jet meant to operate from fixed airbases the runway length required for landing was considered adequate.


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What are these Lights on the Center Column between Cockpit Windows on the A320?
I have always noticed there is what appears to be three lights on the center column, which separates the pilot and copilot window of the Airbus A320 family. From the looks, the center light is red and two surrounding lights are white. They also seem to be present in other aircraft, like the A350. Though there they are far less visible and integrate more smoothly into the background colors.
My question is: What are those for? I have checked the FCOM and the internet but I could not find any information on them. See the image below, for the lights I am referring to.

These are not lights, they are the Eye Reference Indicators. They are used to find the correct seating position. You adjust your seat such that the white ball is exactly hidden behind the red ball on your side:

Since the A300 Airbus has provided an eye reference indicator on the centre structure of the windshield in all Airbus aircraft (fig.3). It enables flight crew to adjust their seat position so that their eyes position matches the eye reference point. The indicator is a device that is fitted with 3 balls painted red or white. To achieve a correct seating position, pilots must align the red and white ball meaning that the white ball is hidden when in the correct position.

(Airbus - Are You Properly Seated?)
This YouTube video shows how to properly adjust your seat on the A320 (you can see the eye reference indicators at around 1:30): CORRECT COCKPIT SEAT POSITION! Eye-Position-Indicator explained by "CAPTAIN" Joe
They are not unique to Airbus though, some other aircraft have them too, like e.g. the ATR-72 (left) or the Dash-8 Q400 (right):

(image source: theflyingengineer.com)
Boeing uses a different method for seat adjustment, so you won't find such indicators there.

Almost like PAPI for pilots' eyes

@Bianfable thank you! That's an excellent answer and explication. I have marked it as such and upvoted it.

@Accounting https://aviation.stackexchange.com/q/5170/3427

@Fattie To actually answer your question: Yes, the seats are powered. You can see it in operation in the video I linked ;)

@Accounting precision approach path indicator

@DeepSpace that's the first thing that came to  my mind :P

heh thanks @Bianfable - good one


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Is this angle of attack animation backwards?
Is this animation of the angle of attack sensor in this video from 25:30 to 25:50 correct?  It seems like motion of the sensor is the opposite of what it should be based on the angle of the aircraft.  For example, given an angle of attack sensor mounted on the right-hand side of the aircraft, I would suspect that a strong nose-up attitude would cause the blade on the aoa sensor to turn slightly clockwise with respect to the body of the aircraft.  But to me the animation displays a counter clockwise turning for the nose-up attitude.

Looks right to me. Remember that AoA and the angle of the aircraft relative to the horizon are two different things.

Is it possible to add enough information in your post to make it more standalone? As it is we don't have any idea of what you have seen on Youtube.

I think a screenshot of the video with the aircraft pitching up or down would be very helpful, to make this question self-contained.

Maybe, depending on your interpretation.
The animation leaves room for interpretation. It is never specified what remains constant and what changes throughout the animation. For example, is the animation just zooming in on the sensor (and the sensor vane movement is just the entire aircraft pitching), or is the sensor picture relative to the aircraft pitch? Let's assume the latter; in the former case, it's obviously correct but doesn't teach us anything.
Climb/descent interpretation
The aircraft pitch displayed is the actual aircraft pitch as it is in flight. This means that respectively the situation in climb and in descent is shown. This makes sense with the preceding comments about the vane "being stuck in the climb position". In this interpretation, the animation is correct.
As the plane climbs, the thrust vector has a downwards component. This means the aircraft thrust accounts for part of the gravity, and the wings have to take less of the aircraft's weight. This means the angle of attack is reduced in climb, and indeed the sensor vane will point more 'down' during climb, and more 'up' during descent.
Angle of attack interpretation
The pitch shown in the animation corresponds to an angle of attack (i.e., the air mass is moving strictly horizontally through the animation). In this case the animation is incorrect.
A high angle of attack means that the air has a vertical component w.r.t the aircraft body; specifically, from the belly upwards. The AoA vane is like a weathervane, and will follow this movement. In a high AoA situation, it will point up (in a cobra maneuver, it would point straight up). This is opposite from the animation.

No.
The video makes the angle of attack indicator appear to move backwards because of how we perceive movement.  The indicator in the front is moving with respect to the aircraft; at least that is how we perceive it.
In reality, the angle of attack indicator is stationary (with respect to the relative wind) and the fuselage is rotating around the indicator.  The perspective is backwards from what we perceived in the video.


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How much earlier/later is sunrise/sunset at 40,000 feet?
If I'm over New York City, and sunrise is 6am, I will see the sunrise earlier when I'm at 40,000 feet on the plane.
I think that latitude plays a role here, but using NYC as an example, how much earlier/later (later for sunset, as I will see the sun for a longer period at that height) are these events on a plane than on the ground?

You are right. earth sphericity make the horizon farther. sunrise is when sun appear at the horizon. I believe for your religion taking the official sunrise time on ground as a reference should be OK.

@ManuH my question is how to calculate how much earlier or later the sun rises or sets

This is purely a geometry question. Maybe you should try http://math.stackexchange.com/

@J.Hougaard even if it is purely geometry, tha answer (and its consequences) may be useful for this community.

Most religions have exceptions and 'rules of thumb' for people who can't observe rituals as usual, because of illness, travel etc. Asking your religious leader is probably best here, because it sounds like your primary concern is religious, not physical.

@Pondlife leaving the theological discussion out, I am asking how much earlier or later events are at 40,000 feet, not what my religious leader might or might not say about the situation. Most leaders in my religion say to go by where one is relative to the ground. That requires figuring out where you are and what time sunrise is. Im asking how to figure that out.

"The variation with altitude is approximately linear, and so we conclude that sunset is later by 1 minute for every 1.5 kilometres in altitude, and that sunrise is earlier by the same amount."
http://curious.astro.cornell.edu/about-us/161-our-solar-system/the-earth/day-night-cycle/189-how-do-sunrise-and-sunset-times-change-with-altitude-intermediate

@Bitrex expand that into an answer and it looks good enough to be accepted. Thanks!

@MENNyg I believe that there are programs outthere to figure these things out. Myzmanim.com and Chai tables come to mind

@Bitrex you should put your comment as an answer. Even if it is only an approximation, it is a good one and I think it is enough for to answer the question.

Also not speed and direction can affect it (a little), example if plane is heading sunrise at mach 0.8

There's two parts to the answer.  One is the extra angular distance to the sun you get from altitude and the other is the time that it would take to traverse that distance.
For the angular distance, besides the surface geometry, there's some additional effects of refraction.  I'm going to ignore that on the assumption that there will be some refraction both at the surface and at altitude, so it will mostly cancel out (and it's harder to calculate it).
From the surface we see the sun cross a line of 90 degrees to the vertical (horizontal), from 40,000 feet it would be $\sin^{-1}(\frac{R}{R + 40,000 \text{feet}})$ or 86.5 degrees.  From altitude, we see around an extra 3.5 degrees.
The time you get from that extra distance depends on the season and the latitude.  If you were doing it over the arctic circle in december, you might get hours or days more sunlight.
If you have time to look it up, check the civil twilight calculator for your location.  That's the time when the sun is 6 degrees below the horizon.  That means you'd see sunset at that altitude about the midpoint of civil twilight.
Otherwise, you can make a broad guess that most places in mid-latitudes have a civil twilight that lasts about half an hour.  So at altitude, you get about 15 more minutes.  Maybe a couple minutes more near solstices, a couple minutes less near equinoxes.


text:
Why does the Information Manual say "C172S - Flaps 10 (Preferred) for Normal Takeoff", when the models before S-model do not have this note?
Do Flaps 10 really do anything performance-wise other than reducing ground roll and distance over a 50-foot obstacle? If not worried about clearing an obstacle, does a Flaps UP-normal takeoff make more sense (Better climb performance since no drag from Flaps) in the C172S?

I think it was because of the power increase in the SP gave flaps 10 climb performance as good as or better than flaps up in the 160 hp version, so make that the standard TO setting and benefit from the shorter run.  Not sure tho.

"Why does the say" I think you're missing a word or two there... Please [edit] to clarify

Related

The Cessna 172S has more power (180hp vs 160hp for 172R) and higher MTOW
(2550lb vs 2400lb for 172R).
This means that folks used to rotating at 55 knots IAS in earlier models would be closer to stall if taking off "clean".  Another way of doing it would be to add 5 knots and rotate clean at 60 knots.
Vx is also a bit higher in the 172S at 62 knots IAS.
Vy is at 74 knots and Vbg is still at 65 knots, indicating few changes aerodynamicly, just a bit more weight requiring more airspeed to generate adequate lift, or flaps can be added to increase lift coefficient at a lower airspeed.